In a Long Term Evolution (LTE) system, Orthogonal Frequency Division Multiplexing (OFDM) is adopted to modulate the high-speed data to each orthogonal subchannel, so mutual interference between channels can be effectively reduced. However, OFDM is only applied to the user equipments in the current cell. Owing to frequency-division multiplexing between cells, interference exists between user equipments of different cells, thus result in a poor performance near the edge of a cell, and so interference between cells becomes main interference in an LTE system.
In order to solve the problem of poor performance near the edge of a cell, the 3rd Generation Partnership Project (3GPP) introduces Inter Cell Interference Coordination (ICIC) technology and Coordinated Multiple Points (CoMP) technology in version R8 specification and version R11 specification to improve the performance of user equipments near a cell edge. Where CoMP technology can provide service to user equipments near a cell edge through coordination between a plurality of adjacent base stations or nodes, so as to reduce the co-channel interference to the user equipments near a cell edge and improve the service quality to the user equipments near a cell edge. According to the different degrees of sharing of user data and channel state information, CoMP technology is further divided into Joint-Processing (JP) technology and Coordinated Scheduling/Beamforming (CS/CB) technology.
The basic principle of coordinated beamforming (CB) transmission technology is that: for the User Equipments (UEs) with poor signal quality in the cell edge, beamforming of Physical Downlink Shared Channel (PDSCH) needs to be finished with the joint participation of a coordinated cell. Specifically, scheduling information and channel state information of a CoMP UE and a coordinated UE is interacted between a serving cell and a coordinated cell, the CoMP UE and coordinated UE can adjust their respective shaped-beam based on the information to make the shaped-beams orthogonal as much as possible, thereby reducing the mutual beam interference.
There are mainly two schemes to realize coordinated beamforming in the prior art as follows.
SLNR scheme: adopting Signal-to-Leakage-and-Noise Ratio (SLNR) algorithm. A CoMP UE and a coordinated UE determine their respective beamforming vector with the maximum value of ratio of their respective useful signal strength to the interference signal strength to other UEs as the criterion, so as to guarantee the minimum interference to other UEs on the premise of ensuring the performance of the CoMP UE and the coordinated UE, thereby reducing the co-channel interference to the UEs near a cell edge. Theory of the algorithm can maximize the performance of CB, but the complexity of computation is very high, the beamforming vector of the CoMP UE and the coordinated UE needs to be adjusted, and the serving cell and coordinated cell need to exchange scheduling information and channel state information mutually, which can cause excess transmission delay; therefore, the scheme is seldom adopted in product realization.
Beamforming orthogonalization adjustment scheme: the beamforming vector of the CoMP UE is not adjusted; the beamforming vector of the coordinated UE is adjusted based on the scheduling information and channel state information of the CoMP UE, and null steering of the beam is directed at the channel of the CoMP UE, thereby reducing the interference to the CoMP UE. The scheme is the product realization scheme mainly adopted by mainstream equipment manufacturers, but the major problem is that after adjustment of beamforming vector of the coordinated UE, energy and direction of the shaped-beam are not optimal, so the performance of the coordinated UE may decline.
In addition, for a scenario that a plurality of CoMP UEs request for coordination from the same coordinated cell, the conflict that the plurality of CoMP UEs request coordination simultaneously may occur. No effective solutions have been provided in the prior art.